1. Field of the Invention
The present invention relates to a method for manufacturing a printed circuit board with a thin film capacitor embedded therein using laser lift-off, and more particularly, to a method for manufacturing a printed circuit board with a thin film capacitor embedded therein which has a dielectric film using laser lift off, and a printed circuit board with a thin film capacitor embedded therein manufactured thereby.
2. Description of the Related Art
With a smaller, lighter, higher-speed and higher-frequency trend of electronic devices, the electronic devices are increasingly required to possess higher-density. In reality, vigorous studies have been conducted on technologies to integrate passive and/or active devices into a substrate. Also, in ongoing researches to reduce size of the electronic devices, many passive devices such as a resistor, a capacitor and an inductor are embedded in a printed circuit board (PCB) instead of being installed thereon. Out of these passive devices, the capacitor accounts for a considerable proportion of about 60%. Thus, much attention is drawn on an embedded capacitor. As described above, the capacitor is embedded in the PCB instead of being installed thereon. This downscales size of the passive device by 40% and assures better electrical properties at a higher frequency due to low impedance (<10 pH).
The conventional embedded capacitor is disclosed in U.S. Pat. No. 5,261,153. The document teaches a method for manufacturing a printed circuit board with a capacitor embedded therein by lamination of conductive foils and uncured dielectric sheets alternating therewith. Moreover, U.S. Pat. No. 6,541,137 discloses a high temperature thin film embedded capacitor using dielectrics. Specifically, the document proposes a barrier layer for preventing the conductive layer from oxidizing from high temperature heat treatment of 400° C.□ to 800° C.
However, in this embedded capacitor, a dielectric film is necessarily made of a dielectric material having a high dielectric constant selected from a group consisting of barium strontium titanate (BSTO), barium titanate (BT), lead zirconium titanate (PZT), barium zirconium titanate (BZTO), and tantalum titanate (TTO). This dielectric material should be excellent in crystallinity to exhibit high dielectric constant. To this end, the dielectric material should be heat-treated at a temperature of 500° C. or more.
But in the conventional embedded capacitor, a thin film is formed on an electrode as an RCC type and crystallized through heat treatment to impart a certain dielectric constant to a capacitor product. Then these materials are employed in a PCB process. However, the materials need heat-treating at a high temperature of 400° C. to 800° C., and are hardly configured on a resin-containing PCB.
Dielectric properties of the thin film capacitor are greatly affected by the type of the substrate, as is apparent from FIG. 1. FIG. 1 demonstrates capacitance of a Pb-based dielectric film deposited on two types of substrates with respect to a voltage applied. A copper foil and a Pt/Ti/SiO2/Si substrate are adopted for the substrates, and heat treated in the air at 650° C. for 30 minutes. The dielectric film is deposited to a thickness of 0.6 micrometer. The dielectric film on the cooper foil exhibits capacitance of 0.2 μF/cm2, much lower than the dielectric film on the Pt/Ti/SiO2/Si substrate whose capacitance is 2.5 μF/cm2. The dielectric film deposited on the copper foil is affected by an oxidized interface resulting from oxidation of the copper foil which is heat-treated along with the substrate. This prevents the dielectric film on the copper foil from manifesting properties peculiar to the dielectric material.
Therefore, studies have been conducted unceasingly to prevent the copper foil from oxidization in two methods. That is, a heat-treatment atmosphere has been regulated or a strong oxidation-resistant nickel layer has been formed on the copper foil to deposit and heat-treat the dielectric film. These methods however entail a problem of decreased capacitance of the capacitor manufactured.
As a result, there has arisen a demand for developing a method for manufacturing a capacitor with a printed circuit board embedded therein having a dielectric film that needs heat-treating at a high-temperature through a general PCB manufacturing process.